Articles to be used for various applications, such as wafers to be used for the production of semiconductors, masks to be used in photolithography, plated products, optical parts such as lenses, parts of liquid crystal display devices, or various electronic parts, are usually cleaned by being washed with water such as pure water or rinsed with water such as pure water after being washed with an aqueous cleaning agent or a semi-aqueous cleaning agent in their production processes. In such a case, if water remains on the surface of such an article after the cleaning, it is likely to cause a defect on appearance due to formation of stains or a defect in performance due to formation of rust. Accordingly, it is important to completely remove water from the surface of the article.
As a method for removing such water, a method is known wherein the article to be cleaned is dipped in a solvent capable of removing water from the surface of the article to be cleaned, and after taking it out, the solvent is dried. As the solvent to be employed in this method, an alcohol such as ethanol or isopropyl alcohol is known. However, such an alcohol is a compound having a flash point, and accordingly, it was required to pay attention to the working environment. Further, as such a solvent, a solvent composition is also known which has an alcohol or a surfactant added to a chlorofluorocarbon (hereinafter referred to as CFC). However, CFC is a compound, the production of which has been completely banned since 1996 in developed countries, since its influence to ozone depletion in the stratosphere was pointed out.
As a substitute for CFC, hydrochlorofluorocarbons (hereinafter referred to as HCFC), hydrofluorocarbons (hereinafter referred to as HFC) or hydrofluoroethers (hereinafter referred to as HFE) have, for example, been developed, and solvent compositions having alcohols added to such compounds, have been proposed also in applications to removal of water after the cleaning as mentioned above.
Such a solvent composition shows good water removal performance at the initial stage, but has had a problem that when it is used for a long period of time continuously, water is taken into the solvent compositions and suspended. Namely, for the purpose of removing water in a short time when the article to be cleaned is dipped in the solvent composition, a method of forcibly stirring water by ultrasonic cleaning, vibration cleaning or jet cleaning, or for the purpose of removing water surfaced to the liquid surface in the dipping tank for dewatering, a means to recycle the solvent composition may be provided, whereby water is forcibly stirred to form a suspension.
If the proportion of water suspended in the solvent composition becomes large, water tends to remain on the surface of the article to be cleaned, thus leading to a problem of formation of stains on the object to be cleaned.
As a method to solve such a problem, a method has been proposed wherein a porous fluororesin paper which permits a solvent to pass therethrough but does not permit water to pass therethrough, is disposed in the flow path of the solvent after treatment for removal of water, to prevent passage of water suspended in the solvent thereby to separate the water (JP-A-2002-355502). However, such a method has a problem that in a case where the proportion of water suspended in the solvent is high, the speed of the solvent passing through the porous fluororesin paper tends to be low, and when the solvent composition is recycled, an adequate amount of recycling can not be maintained.